Methods Relating to Designing Wellbore Strengthening Fluids

ABSTRACT

Generally, assessing the properties of a plug comprising wellbore strengthening materials may enable the design of more efficient wellbore strengthening additives and fluids because the properties of the plug may translate to the near wellbore strengthening effect of the wellbore strengthening materials of the plug. Assessing such properties may involve applying a differential pressure to a plug formed in a passageway of a tool comprising at least one sensor proximal to the passageway plug, and then measuring at least one attribute selected from the group consisting of a normal plug pressure, a normal plug displacement, and any combination thereof with the at least one sensor.

BACKGROUND

The present invention relates to the design of wellbore strengtheningadditives and fluids based on the assessment of the properties of a plugcomprising wellbore strengthening materials, including methods,apparatuses, and systems relating thereto. Generally, the properties ofthe plug may translate to the near wellbore strengthening effect of thewellbore strengthening materials of the plug.

Lost circulation is one of the larger contributors to non-productivedrilling time. Lost circulation arises from drilling fluid leaking intothe formation via undesired flow paths, e.g., permeable sections,natural fractures, and induced fractures. Lost circulation treatmentsmay be used to remediate the wellbore by plugging the undesired flowpaths before drilling can resume.

Drilling, most of the time, is performed with an overbalance pressuresuch that the wellbore pressure (equivalent circulating density) ismaintained within the mud weight window, i.e., the area between the porepressure (or collapse pressure) and the fracture pressure, see FIG. 1.That is, the pressure is maintained high enough to stop subterraneanformation fluids from entering the wellbore and low enough to not createor unduly extend fractures surrounding the wellbore. The term“overbalance pressure,” as used herein, refers to the amount of pressurein the wellbore that exceeds the pore pressure. The term “porepressure,” as used herein, refers to the pressure of fluids in theformation. Overbalance pressure is needed to prevent subterraneanformation fluids from entering the wellbore. The term “fracturepressure,” as used herein, refers to the pressure threshold wherepressures exerted in excess of the fracture pressure from the wellboreonto the formation will cause one or more fractures in the subterraneanformation. Wider mud weight windows allow for drilling with a reducedrisk of lost circulation.

In traditional subterranean formations, the mud weight window may bewide, FIG. 1. However, in formations having problematic zones, e.g.,depleted zones, high-permeability zones, highly tectonic areas with highin-situ stresses, or pressurized shale zones below salt layers, whichare often found in formations with a plurality of lithographies, the mudweight window may be narrower and more variable, FIG. 2. When theoverbalance pressure exceeds the fracture pressure, a fracture isexpected to be induced, and lost circulation may occur. One proactivemethod of reducing the risk of lost circulation is to strengthen orstabilize the wellbore through the use of wellbore strengtheningmaterials. One method of wellbore strengthening involves inducingfractures while simultaneously plugging the fractures. This simultaneousfracture-plug method increases the compressive tangential stress in thenear-wellbore region of the subterranean formation, which translates toan increase in the fracture initiation pressure or fracture reopeningpressure, thereby widening the mud weight window, FIG. 3. The extent ofwellbore strengthening, i.e., expansion of the mud weight window, couldbe a function of the properties of the plug in terms of its ability towithstand higher pressures, among others as described in this invention.If the plug fails, lost circulation and drilling non-productive timeresults.

The strength of the plug may depend on, inter alia, keeping the inducedfracture propped open and/or preserving the increased circumferential(hoop) stress that was required to open the fractures and/or isolatingthe fracture tips from the fluid and pressure of the wellbore. FIG. 4provides an illustration of some of the downhole pressures relating towellbore strengthening. FIG. 4 also illustrates isolation of thefracture tips from the wellbore by plugs comprising wellborestrengthening materials. Understanding how plugs comprising wellborestrengthening materials react to the various pressures experienced in awellbore may advantageously allow for the design of wellborestrengthening fluids or additives thereof that better strengthen thewellbore, thereby minimizing fluid loss and consequently reducing rigdowntime and costs.

SUMMARY OF THE INVENTION

The present invention relates to the design of wellbore strengtheningadditives and fluids based on the assessment of the properties of a plugcomprising wellbore strengthening materials, including methods,apparatuses, and systems relating thereto. Generally, the properties ofthe plug may translate to the near wellbore strengthening effect of thewellbore strengthening materials of the plug.

In one embodiment of the present invention, a method may comprise:providing a fluid comprising a wellbore strengthening material; passingthe fluid through a passageway of a tool comprising at least one sensorproximal to the passageway so as to form a plug that comprises thewellbore strengthening material in the passageway; applying adifferential pressure to the plug in the passageway; and measuring atleast one attribute selected from the group consisting of a normal plugpressure, a normal plug displacement, and any combination thereof withthe at least one sensor.

In another embodiment of the present invention, a method may comprise:providing a first fluid comprising a first wellbore strengtheningmaterial; passing the first fluid through a passageway of a toolcomprising at least one sensor proximal to the passageway so as to forma plug that comprises the first wellbore strengthening material in thepassageway; applying a differential pressure to the plug in thepassageway; measuring at least one attribute selected from the groupconsisting of a normal plug pressure, a normal plug displacement, andany combination thereof with the at least one sensor; deriving at leastone value selected from the group consisting of sustained increased hoopstress, compressive strength of the plug, shear strength of the plug,and any combination thereof from the at least one attribute; anddeveloping a wellbore strengthening additive comprising a secondwellbore strengthening material based on the at least one value.

In yet another embodiment of the present invention, a tool may comprisean implement that comprises at least one passageway that models anopening in a subterranean formation, the passageway comprising an entryport on a first end of the object, an exit port at an opposing end of anobject, and a wall extending from the entry port to the exit port; andat least one sensor in or on the implement proximal to the wall of thepassageway.

The features and advantages of the present invention will be readilyapparent to those skilled in the art upon a reading of the descriptionof the preferred embodiments that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures are included to illustrate certain aspects of thepresent invention, and should not be viewed as exclusive embodiments.The subject matter disclosed is capable of considerable modifications,alterations, combinations, and equivalents in form and function, as willoccur to those skilled in the art and having the benefit of thisdisclosure.

FIG. 1 illustrates the mud weight window for a traditional wellbore.

FIG. 2 illustrates the mud weight window for a problematic wellbore.

FIG. 3 illustrates the mud weight window for a strengthened wellbore.

FIG. 4 illustrates some of the downhole pressures relating to wellborestrengthening.

FIG. 5 provides a nonlimiting representation of a Tapered Cell, notnecessarily to scale.

FIGS. 6A-E provide cross-sectional illustrations of nonlimiting examplesof tool/sensor configurations.

FIGS. 7A-B provide a cross-section and top view, respectively, of a toolhaving a plurality of node sensors embedded in the tool proximal to thepassageway of the tool.

FIGS. 7C-D provide a cross-section and top view, respectively, of a toolcomprising a holder and an insert, where the insert has two layers witha plurality of wire sensors embedded in the insert layer proximal to thepassageway of the tool.

FIG. 8A provides a nonlimiting illustration of a plug exerting a normalplug pressure on a passageway of a tool having sensors.

FIG. 8B provides a nonlimiting illustration of a plug exerting a normalplug displacement on a passageway of a tool having sensors.

FIG. 9 provides a nonlimiting representation of a Pore PluggingApparatus, not necessarily to scale.

FIGS. 10A-C provide illustrations of suitable pressure applicationprocedures that may be applied to a plug while measuring a normal plugpressure and/or normal plug displacement of the plug.

DETAILED DESCRIPTION

The present invention relates to the design of wellbore strengtheningadditives and fluids based on the assessment of the properties of a plugcomprising wellbore strengthening materials, including methods,apparatuses, and systems relating thereto. Generally, the properties ofthe plug may translate to the near wellbore strengthening effect of thewellbore strengthening materials of the plug.

The present invention provides for, in some embodiments, systems andapparatuses for assessing the wellbore strengthening capabilities ofwellbore strengthening materials (WSM). By better understanding thecharacteristics and capabilities of individual WSM and/or combinationsof WSM, wellbore strengthening fluids could be designed to provideimproved wellbore strengthening, e.g., a greater or sustained increasein the mud weight window with stronger plugs of WSM and fluids andadditives that achieve mud weight window expansions more efficiently,especially in subterranean formations with a plurality of lithographieswhere the interface between two lithographies can create a section ofthe wellbore that is more susceptible to fracture and fluid loss.Accordingly, the present invention also provides for, in someembodiments, methods relating to the assessment of the WSM includingmethods that extend to the design of a wellbore strengthening fluid oradditive thereof based on the assessment.

Greater or efficient wellbore strengthening may also provide for, insome embodiments, the capability to safely drill longer sections of awellbore, which translates to less non-productive time and decreasedcosts. Further, longer drilled sections enable longer casing sections.Because each subsequent casing section is at a smaller diameter than theprevious section, greater wellbore strengthening may ultimately allowfor deeper wellbores and the capabilities to access previously untappedresources.

During drilling and other operations in an uncased wellbore, thewellbore can experience pressure surges as a result of, inter alia,initiating flow of a static or near static fluid and running drill pipeor casing. These pressure surges may briefly exceed fracture pressure ofa portion of the subterranean formation and cause a point of fluid lossto form (e.g., a fracture or a microfracture). Strengthening a wellboremay mitigate induced points of fluid loss, which consequently mitigatesthe need for remedial treatments and nonproductive time.

Generally, after a section of the wellbore has been drilled, a casing isapplied to the surface of the subterranean formation along the wellboreso as to prevent collapse of the wellbore, damage to the subterraneanformation, fluid loss into the subterranean formation, and the likewhile additional wellbore sections are drilled. One method of casing awellbore includes displacing the drilling fluid with a higher densityfluid and then cementing. During the displacement of the drilling fluid,the uncased wellbore may be susceptible to damage, e.g., formation of apoint of fluid loss, because the higher density fluid yields anoverbalance pressure that is generally closer to the fracture pressure.Widening the mud weight window may advantageously mitigate and/orprevent the formation of a point of fluid loss during fluid displacementand casing operations.

Additionally, after a casing is set in a wellbore, the location in thewellbore that transitions from cased wellbore to uncased wellbore (e.g.,the location of a casing shoe) may be one of the weakest points in thewellbore (i.e., the area with the greatest potential to fracture andcause fluid loss into the formation). In some operations, WSM isintroduced into the wellbore first at higher concentration to create a“strong shoe” by strengthening the portion of the wellbore thattransitions from cased to uncased. The present invention provides for,in some embodiments, developing wellbore strengthening fluids that maybe capable of producing shoes with higher strengths and longerlifetimes. Enhanced shoes that strengthen wellbores at the transitionfrom cased to uncased further provide for the benefits enumerated above,like the capability to safely drill longer sections of a wellbore.

It should be noted that when “about” is provided at the beginning of anumerical list, “about” modifies each number of the numerical list. Itshould be noted that in some numerical listings of ranges, some lowerlimits listed may be greater than some upper limits listed. One skilledin the art will recognize that the selected subset will require theselection of an upper limit in excess of the selected lower limit.

For simplicity, the term “test wellbore strengthening materials” (TWSM)as used herein refers to the WSM used in conjunction with measuring aproperty of a plug comprising the WSM with a tool of the presentinvention. Then, as used herein the term “designed wellborestrengthening materials” (DWSM) refers to the WSM used in wellborestrengthening fluids for use in wellbore operations based on theproperty of the plug comprising a TWSM (including any value derivedtherefrom, which are described in more detail below). It should be notedthat the terms TWSM and DWSM should not be seen as limiting or exclusivecompositions. That is, any WSM may be used as a TWSM or a DWSM.

Some embodiments may involve measuring a property of a plug comprisingat least one TWSM using a Pore Plugging Apparatus, wherein the plug islodged in a passageway of a tool of the present invention.

As used herein, the term “tool” refers to an implement that comprises atleast one passageway extending from a first end through to an opposingend of the implement, where the passageway models an opening in asubterranean formation (e.g., a pore, a fracture, or a microfracture).As used herein, the term “Pore Plugging Apparatus” refers generally toan apparatus and/or system capable of applying differential pressuresacross passageway of a tool so as to form a plug in the passagewayand/or apply differential pressures to a plug lodged in the passagewayof the tool, and is described in more detail below.

A passageway is generally defined by an entry port, an exit port, andwalls. In some embodiments, a passageway may be synthetic (e.g.,machined or caused by applying pressure to a small opening formed in thetool), native (e.g., a natural fracture in a core sample), or acombination thereof (e.g., a natural fracture that was syntheticallyextended to have both an entry port and exit port).

In some embodiments, the entry and exit ports of a passageway may besubstantially the same shape but sized differently. In some embodiments,a tool of the present invention may have a passageway with an entry portand an exit port with a shape of a slit (i.e., a substantiallyrectangular shape that is at least 50 times greater in length thanwidth), an artificial or man-made fracture, or any hybrid thereof.

A suitable tool of the present invention may, in some embodiments, havea synthetic passageway with an entry port with the smallest dimensionbetween about 1000 microns and about 6000 microns, an exit port with thesmallest dimension between about 100 microns and about 3000 microns, anda length (i.e., the distance between the entry port and the exit port)between about 5 cm and 20 cm. One skilled in the art with the benefit ofthis disclosure should understand the size and shape of the syntheticpassageway of a tool of the present invention may depend on, inter alia,the type of formation or formation microfractures where WSM may beemployed in wellbore strengthening operations.

By way of nonlimiting example, a passageway may be a tapered slot.Generally, a tapered slot is a synthetic passageway with walls thattaper from the size and shape of the entry port to the size and shape ofthe exit port. The tapering may be at a constant angle, at two or moreangles with a sharp transition between angles, at two or more angleswith a smooth transition between angles (e.g., rounded transitions), orany hybrid thereof. A nonlimiting example of a tool of the presentinvention having a tapered slot passageway is illustrated in FIG. 5 withan entry point 2500 microns across and exit point 1000 microns across.

In some embodiments, the walls (or at least one wall) of a passageway ina tool of the present invention may be adjustable so as to allow forchanging the distance between opposing walls. Depending on theconfiguration of the adjustable walls, the entry port and/or exit portmay also be adjustable so as to provide for adjustment of the smallestdimension of the entry port and/or exit port.

In some embodiments, a tool of the present invention may comprise aholder and insert capable of operably mating with a holder. A tool ofthe present invention comprising a holder and insert may advantageouslyallow for changing the dimensions of the passageway with greater easeand at less expense. Further, the incorporation of sensors in an insert,as described below, may advantageously provide for easier maintenanceand care of the sensors including replacement of a sensor.

In some embodiments, measuring a property of a plug lodged in apassageway of a tool of the present invention may be achieved using atleast one sensor coupled to the tool. A sensor coupled to a toolincludes, but is not limited to, a sensor embedded in at least a portionof the tool, a sensor embedded in at least a portion of a toolcomponent, a sensor disposed on at least a portion of the tool, a sensordisposed on at least a portion of a tool component, or any hybridthereof.

FIGS. 6A-E provide cross-sectional illustrations of nonlimiting examplesof tool/sensor configurations where hashmarks illustrate at least someof the locations a sensor may be coupled to a tool. FIG. 6A provides atool cross-section illustrating that a sensor may be embedded in thetool proximal to the passageway of the tool. FIG. 6B provides a toolcross-section illustrating that a passageway wall may have a layerdisposed thereon that the sensor is coupled to. FIG. 6C provides a toolcross-section illustrating that a passageway may have multiple layerswere the sensor is coupled to a layer other than the layer proximal tothe passageway. FIG. 6D provides a tool cross-section illustrating atool comprising a holder and an insert, where the insert has more thanone layer and the sensor may be coupled to a layer other than the layerproximal to the passageway. FIG. 6E provides a tool cross-sectionillustrating a tool comprising a holder and an insert, where the inserthas more than one layer and the sensor may be coupled to a layerproximal to the passageway.

Suitable sensors for use in conjunction with a tool of the presentinvention may include, but are not limited to, force gauges, load cells,piezoelectric sensors, strain gauges, temperature gauges, temperaturesensors, magnetic sensors, ultrasonic sensors and the like, or anyhybrid thereof. Sensors for use in conjunction with a tool of thepresent invention may be in the form of sensor nodes, an array of sensornodes, a wire sensor, a plate sensor, and the like, any hybrid thereof,or any combination thereof. Sensors for use in conjunction with a toolof the present invention may communicate with an output device (e.g., acomputer, a display, and the like) through wires, wirelessly, or anycombination thereof.

One skilled in the art, with the benefit of this disclosure, shouldunderstand the plurality of configurations that a tool of the presentinvention may comprise a sensor in a suitable location. By way ofnonlimiting example, FIGS. 7A-B include a cross-section and top view,respectively, of a tool having a plurality of node sensors embedded inthe tool proximal to the passageway of the tool, such that the pluralityof sensors are arranged in a regular array along the height and width ofthe two long walls making up the passageway having an oblongcross-section. By way of another nonlimiting example, FIGS. 7C-D includea cross-section and top view, respectively, of a tool comprising aholder and an insert, where the insert has two layers with a pluralityof wire sensors embedded in the insert layer proximal to the passagewayof the tool.

Suitable plug properties that may be measured in a tool of the presentinvention may include, but are not limited to, a normal plug pressureand/or normal plug displacement. As used herein, the term “normal plugpressure” refers to the pressure exerted by a plug that is lodged in apassageway onto the walls of the passageway of the tool of the presentinvention. It should be noted that “normal plug pressure” is not limitedto pressure exerted only at a 90° angle from the walls of thepassageway, but rather is a more general term referring to pressure atany angle exerted from the plug onto the wall of the passageway. As usedherein, the term “normal plug displacement” refers to the maximumdistance a wall of a passageway of a tool of the present invention isdisplaced by a plug lodged in the passageway at a given pressure and/ordifferential pressure.

Some embodiments may involve measuring a normal plug pressure and/ornormal plug displacement at a plurality of differential pressuresexerted on the plug in the passageway direction. FIG. 8A provides anonlimiting illustration of a plug lodged in a passageway of a toolhaving sensors, where the sensors are capable of measuring the normalplug pressure at a given differential pressure exerted in the passagewaydirection, where the pressure towards the exit port of the passageway isgreater than the pressure towards the entry port of the passageway. FIG.8B provides a nonlimiting illustration of a plug lodged in a passagewayof a tool having sensors, where the sensors are capable of measuring thenormal plug displacement at a given differential pressure exerted in thepassageway direction, where the pressure towards the exit port of thepassageway is greater than the pressure towards the entry port of thepassageway.

Suitable materials that a tool of the present invention, or portionthereof (e.g., a portion of an insert, a holder, or a coating) may beformed of may include, but are not limited to, metal (e.g., stainlesssteel), cork, synthetic cork, a core sample, synthetic core, sandstone,ceramic, resin, polymers, polymer composites, epoxy, or any combinationthereof. Because sensors used in conjunction with the present inventiongenerally measure forces exerted on a wall of a passageway of a tool,the material between the sensor and the surface of the wall may, in someembodiments, advantageously be deformable, reversibly or irreversibly.Suitable deformable materials may include, but are not limited to, cork,synthetic cork, resins, polymers, polymer composites, epoxies, or anycombination thereof.

In some embodiments, the material that forms a tool of the presentinvention, or portion thereof, may have a permeability ranging from alower limit of impermeable, 1 nD, 10 nD, 25 nD, 50 nD, 100 nD, or 500 nDto an upper limit of about 10 milliDarcy (mD), 1 mD, 500 microD, 100microD, 10 microD, or 500 nD, and wherein the permeability may rangefrom any lower limit to any upper limit and encompass any subsettherebetween. By way of nonlimiting example, a stainless steel tool maybe impermeable, while a tool made of sandstone may have a permeabilityof about 10 mD. One skilled in the art with the benefit of thisdisclosure should understand the choice of a permeability of thematerial that forms a tool may depend on, inter alia, the type offormation or formation microfractures where WSM may be employed inwellbore strengthening operations.

Generally, methods of the present invention include, in someembodiments, forming a plug of TWSM in a tool of the present inventionand then applying a pressure or differential pressure to the plug whilemeasuring a normal plug pressure and/or a normal plug displacement ofthe plug of TWSM. In some embodiments, measuring a normal plug pressureand/or a normal plug displacement may occur during formation of theplug.

By way of nonlimiting example, forming a plug may involve a PorePlugging Apparatus, a nonlimiting example of which is illustrated inFIG. 9, comprising in series a 500-mL volume sample cell having amovable piston, a tool having a passageway therethrough with sensoralong the passageway, and an assembly for collecting the filtrate whiletesting (illustrated as supports, a filtrate reservoir, a cap, and valvein FIG. 9). As shown in FIG. 9, the sample cell is positioned such thatpressure may be applied from the bottom so as to push the sample in thesample reservoir through the passageway and collect the filtrate in thefiltrate reservoir above. This inverted configuration may help preventcomponents of the wellbore strengthening fluid that settle during thestatic test from contributing to the performance of the TWSM. Forming aplug in a Pore Plugging Apparatus may generally be achieved by passing afluid comprising a TWSM of interest through an appropriate tool atincreasing differential pressures until a plug is formed, i.e., no wholefluid (e.g., the mud including fluids and solids) is able to passthrough the tool.

Once a plug of TWSM is formed in a tool of the present invention, someembodiments of the present invention may involve applying pressure ordifferential pressure to the plug of TWSM in the Pore PluggingApparatus; and measuring a normal plug pressure and/or normal plugdisplacement of the plug of TWSM. In some embodiments, applying pressureto the plug of TWSM may be done in the same Pore Plugging Apparatus or adifferent Pore Plugging Apparatus. Further, in some embodiments,applying pressure to the plug of TWSM may be done with a fluid otherthan the wellbore strengthening fluid, e.g., a drilling fluid or thebase fluid of a drilling fluid. Using another fluid, especially a fluidnot comprising a TWSM, may advantageously provide for a better analysisof the wellbore strengthening properties of the plug.

By way of nonlimiting example, after the plug is formed in the tool, aPore Plugging Apparatus may be loaded with a drilling fluid that doesnot contain TWSM. Pressure may be applied from the bottom, as describedabove, in 100 psi intervals as illustrated in FIG. 9. At each interval,a normal plug pressure and/or normal plug displacement of the plug maybe measured. Alternatively, a normal plug pressure and/or normal plugdisplacement of the plug may be measured continuously, i.e., duringpressure increases and pressure sustaining. As shown in FIG. 9, thepressure or differential pressure continues through the plug breakpressure, i.e., the pressure at which the plug allows whole drillingfluid to pass through the tapered slot. It should be noted that asdescribed in this example, the Plug Pressure Test involves testing thetool in the Pore Plugging Apparatus in which the plug was formed.However, in some embodiments, the tool may be transferred to a secondPore Plugging Apparatus for testing after the plug is formed.

One skilled in the art with the benefit of this disclosure shouldunderstand the plurality suitable pressure application procedures forapplying pressure or differential pressure to the plug while measuring anormal plug pressure and/or normal plug displacement of the plug.Examples of suitable pressure application procedures may include, butare not limited to, a steady increase in pressure or differentialpressure, an exponential increase in pressure or differential pressure,a step-wise increase in pressure or differential pressure, a steadydecrease in pressure or differential pressure, an exponential decreasein pressure or differential pressure, a step-wise decrease in pressureor differential pressure, any hybrid thereof, or any combinationthereof. By way of nonlimiting example, FIGS. 10A-C provideillustrations of suitable pressure application procedures that may beapplied to a plug while measuring a normal plug pressure and/or normalplug displacement of the plug. FIG. 10A illustrates a pressureapplication procedure including, in order, a steady pressure at theinitial overburden pressure (equal to the fracture pressure), a steadyincrease and then sustained pressure, a steady increase and thensustained pressure, a steady decrease and then sustained pressure, asteady increase and then sustained pressure, and finally a steadydecrease and then sustained pressure greater than the initial overburdenpressure. FIG. 10B illustrates a pressure application procedureincluding, in order, starting from the initial overburden pressure(equal to the fracture pressure) an exponential increase and thenexponential decrease to a sustained pressure greater than the poreforming pressure, a steady decrease and then sustained pressure at thepore forming pressure, and finally an exponential increase and thenexponential decrease to a sustained pressure greater than the overburdenpressure. This pressure application procedure, and others like it, mayadvantageously simulate pressure spikes that may be experienced in awellbore when, for example, pumps are turned on. FIG. 10C illustrates apressure application procedure including, in order, starting from theinitial overburden pressure (equal to the fracture pressure) a briefsustained pressure followed by an exponential increase in pressure,another sustained pressure then an exponential increase in pressurefollowed by a more prolonged sustained pressure, then a steady statedecrease in pressure, and then a repeat of the pressure applicationprocedure. Repetition within a pressure application procedure mayadvantageously provide insight into the durability of a plug comprisingTWSM.

Some embodiments of the present invention may involve forming a plug ofTWSM in a Pore Plugging Apparatus; applying pressure or differentialpressure to the plug of TWSM in the Pore Plugging Apparatus; andmeasuring a normal plug pressure and/or normal plug displacement of theplug of TWSM. Some embodiments of the present invention may involveforming a plug of TWSM in a Pore Plugging Apparatus; applying a seriesof pressures or differential pressures to the plug of TWSM in the PorePlugging Apparatus; and measuring a normal plug pressure and/or normalplug displacement of the plug of TWSM for at least one of the pressuresor differential pressures in the series.

In some embodiments, a normal plug pressure and/or normal plugdisplacement of a plug may be used to calculate a plurality of valuesapplicable to wellbore strengthening, e.g., sustained increased hoopstress, compressive strength of the plug, shear strength of the plug,and any combination thereof. By way of nonlimiting example, acharacteristic of the plug may be used to calculate the range ofwellbore hoop stresses in which a plug of a given WSM composition isoperable. For example, the normal plug pressure may be directlyproportional to near wellbore hoop stress, i.e., increase in the normalplug pressure may translate to increase in the near wellbore hoopstress. Further, the compressive strength of the plug may also beproportional to the normal plug pressure and/or normal plugdisplacement.

In some embodiments, a normal plug pressure, normal plug displacement,and/or values applicable to wellbore strengthening may be used, at leastin part, to determine a relative wellbore strengthening capability for agiven TWSM. As used herein, “relativity,” as it relates to wellborestrengthening capability, refers both to the relative comparison betweentwo or more TWSM and the comparison of one or more TWSM to a wellborestrengthening scale. Because a normal plug pressure, normal plugdisplacement, and/or values applicable to wellbore strengthening, andconsequently the relative wellbore strengthening values, depend on,inter alia, the configuration of the passageway and the tool material, awellbore strengthening capability scale may be dependent on, inter alia,the configuration of the passageway and the material(s) from which thetool or component thereof is made.

Some embodiments of the present invention may involve determining arelative wellbore strengthening value of a TWSM based on, at least inpart, a normal plug pressure, normal plug displacement, and/or valuesapplicable to wellbore strengthening. Further, if measurements of anormal plug pressure and/or normal plug displacement are performed at aplurality of pressures and/or differential pressures, then the pluralityof normal plug pressure, normal plug displacement, and/or valuesapplicable to wellbore strengthening may be used to determine a relativewellbore strengthening value of a TWSM.

Generally, a normal plug pressure, normal plug displacement, and/orvalues applicable to wellbore strengthening of a plug of TWSM and/or arelative wellbore strengthening capability of a TWSM may be used todesign wellbore strengthening fluids and/or wellbore strengtheningadditives.

In some embodiments, wellbore strengthening fluids and/or wellborestrengthening additives may comprise DWSM that are the same or differentthan the TWSM. The similarities or differences may be in thecomposition, the concentration, the relative concentration when two ormore WSM are employed, the size distribution, and the like, or anycombination thereof. By way of nonlimiting example, TWSM may includecarbon fibers with an aspect ratio of about 15 in combination withsilica particles with an average diameter of about 250 microns, whilethe DWSM of a designed wellbore strengthening additive may includecarbon fibers with an aspect ratio of about 15 in combination withsilica particles with an average diameter of about 500 microns. By wayof another nonlimiting example, a series of TWSM may include rayonfibers with differing relative concentrations of resilient graphiticcarbon and ground walnut shells, while the DWSM of a designed wellborestrengthening fluid may include rayon fibers with resilient graphiticcarbon and ground walnut shells in a relative concentration not tested.

Some embodiments may involve introducing a wellbore strengthening fluid(or a wellbore strengthening additive) into at least a portion of awellbore penetrating a subterranean formation, where the wellborestrengthening fluid (or wellbore strengthening additive) comprises DWSM.Some embodiments may involve introducing a wellbore strengthening fluid(or a wellbore strengthening additive) comprising a DWSM into a portionof a wellbore penetrating a subterranean formation so as to produce astrengthened wellbore section.

Some embodiments may involve strengthening at least a portion of awellbore during a drilling operation, i.e., while drilling at least aportion of a wellbore penetrating a subterranean formation. In someembodiments, a drilling fluid may comprise a base fluid and DWSM. Insome embodiments, a drilling fluid may comprise a base fluid and adesigned wellbore strengthening additive. Suitable base fluids fordrilling fluids include suitable base fluids for wellbore strengtheningfluid and are provided further herein.

Some embodiments may involve drilling a wellbore before, after, and/orduring the strengthening of the wellbore. In some embodiments, adrilling fluid not comprising a DWSM may be used before or after awellbore strengthening fluid (or wellbore strengthening additive)comprising a DWSM. In such embodiments, fluids consecutively introducedinto the wellbore may have the same or different compositions and/or thesame or different characteristics, e.g., density and/or weight. Someembodiments may involve substantially removing, e.g., flushing, a fluid(or additive) from the wellbore before introduction of the subsequentfluid. Some embodiments may involve changing the fluid on-the-fly so asto provide for wellbore strengthening with DWSM as needed.

In some embodiments, a drilling fluid used after strengthening awellbore with DWSM may have an increased equivalent circulating densityrelative to a drilling fluid used before strengthening the wellbore.Equivalent circulating density, as used herein, refers to the effectivedensity exerted by a circulating fluid against a formation that takesinto account the pressure drop in the annulus about the point beingconsidered. Equivalent circulating density may be affected by variousparameters including, but not limited to, the viscosity of the drillingfluid, the pump rate, the drilling fluid weight, the annulus size, andany combination thereof. Wellbore strengthening increases thenear-wellbore stresses, e.g., circumferential stresses, which may allowfor a higher mud weight window to be sustained.

In some embodiments, a drilling fluid used after strengthening awellbore with DWSM may have an increased drilling fluid weight relativeto a drilling fluid used before strengthening the wellbore. In someembodiments, the drilling fluid weight may range from drilling fluidweights corresponding to about the pore pressure to drilling fluidweights corresponding to about the fracture pressure. In someembodiments, the drilling fluid weights corresponding to pore pressuremay range from about 2 ppg (pounds per gallon) to about 20 ppg. Thedrilling fluid weights corresponding to fracture pressure can bedetermined with a leak off test, which is commonly known to one skilledin the art, when performed to determine the maximum pressure a formationcan sustain.

Wellbore Strengthening Materials and Wellbore Strengthening Fluids

Suitable WSM for use in conjunction with the present invention mayinclude, but are not limited to, particulates, fibers, and anycombination thereof. The particulate and/or fiber may be natural orsynthetic, degradable or nondegradable, and mixtures thereof. It shouldbe understood that the term “particulate” or “particle,” as used herein,includes all known shapes of materials, including substantiallyspherical materials, crenulated materials, low aspect ratio materials,polygonal materials (such as cubic materials), discus, hybrids thereof,and any combination thereof. It should be understood that the term“fiber,” as used herein, includes all known shapes of materials withmedium to high aspect ratios, including filaments and collections offilaments. In some embodiments, the aspect ratio of a fiber may rangefrom a lower limit of about 5, 10, or 25 to an unlimited upper limit.While the aspect ratio upper limit is believed to be unlimited, theaspect ratio of applicable fibers may range from a lower limit of about5, 10, or 25 to an upper limit of about 10,000, 5000, 1000, 500, or 100,and wherein the aspect ratio may range from any lower limit to any upperlimit and encompass any subset therebetween. In some embodiments, thelength of a fiber may range from a lower limit of about 150, 250, 500,or 1000 microns to an upper limit of about 6000, 5000, 2500, or 1000,and wherein the fiber length may range from any lower limit to any upperlimit and encompass any subset therebetween. Fibers may be swellable,i.e., increase in volume by absorbing solvent. Fibers may be aggregatesof filaments where the aggregate may or may not have a medium to highaspect ratio.

In some embodiments, at least one particulate may be used in combinationwith at least one fiber in a wellbore strengthening fluid. Suitableparticulates and/or fiber may include those comprising materialssuitable for use in a subterranean formation including, but not limitedto, any known lost circulation material, bridging agent, fluid losscontrol agent, diverting agent, plugging agent, and the like, and anycombination thereof. Examples of suitable materials may include, but notbe limited to, sand, shale, ground marble, bauxite, ceramic materials,glass materials, metal pellets, high strength synthetic fibers,resilient graphitic carbon, cellulose flakes, wood, resins, polymermaterials (crosslinked or otherwise), polytetrafluoroethylene materials,nut shell pieces, cured resinous particulates comprising nut shellpieces, seed shell pieces, cured resinous particulates comprising seedshell pieces, fruit pit pieces, cured resinous particulates comprisingfruit pit pieces, composite materials, and any combination thereof.Suitable composite materials may comprise a binder and a filler materialwherein suitable filler materials include silica, alumina, fumed carbon,carbon black, graphite, mica, titanium dioxide, meta-silicate, calciumsilicate, kaolin, talc, zirconia, boron, fly ash, hollow glassmicrospheres, solid glass, and any combination thereof.

In some embodiments, particulates and/or fibers may comprise adegradable material. Nonlimiting examples of suitable degradablematerials that may be used in the present invention include, but are notlimited to, degradable polymers (crosslinked or otherwise), dehydratedcompounds, and/or mixtures of the two. In choosing the appropriatedegradable material, one should consider the degradation products thatwill result. As for degradable polymers, a polymer is considered to be“degradable” herein if the degradation is due to, inter alia, chemicaland/or radical process such as hydrolysis, oxidation, enzymaticdegradation, or UV radiation. Polymers may be homopolymers, random,linear, crosslinked, block, graft, and star- and hyper-branched. Suchsuitable polymers may be prepared by polycondensation reactions,ring-opening polymerizations, free radical polymerizations, anionicpolymerizations, carbocationic polymerizations, and coordinativering-opening polymerization, and any other suitable process. Specificexamples of suitable polymers include polysaccharides such as dextran orcellulose; chitin; chitosan; proteins; orthoesters; aliphaticpolyesters; poly(lactide); poly(glycolide); poly(E-caprolactone);poly(hydroxybutyrate); poly(anhydrides); aliphatic polycarbonates;poly(orthoethers); poly(amino acids); poly(ethylene oxide);polyphosphazenes; and any combination thereof. Of these suitablepolymers, aliphatic polyesters and polyanhydrides are preferred.Dehydrated compounds may be used in accordance with the presentinvention as a degradable solid particulate. A dehydrated compound issuitable for use in the present invention if it will degrade over timeas it is rehydrated. For example, particulate solid anhydrous boratematerial that degrades over time may be suitable. Specific examples ofparticulate solid anhydrous borate materials that may be used include,but are not limited to, anhydrous sodium tetraborate (also known asanhydrous borax) and anhydrous boric acid. Degradable materials may alsobe combined or blended. One example of a suitable blend of materials isa mixture of poly(lactic acid) and sodium borate where the mixing of anacid and base could result in a neutral solution where this isdesirable. Another example would include a blend of poly(lactic acid)and boric oxide, a blend of calcium carbonate and poly(lactic) acid, ablend of magnesium oxide and poly(lactic) acid, and the like. In certainpreferred embodiments, the degradable material is calcium carbonate pluspoly(lactic) acid. Where a mixture including poly(lactic) acid is used,in certain preferred embodiments the poly(lactic) acid is present in themixture in a stoichiometric amount, e.g., where a mixture of calciumcarbonate and poly(lactic) acid is used, the mixture comprises twopoly(lactic) acid units for each calcium carbonate unit. Other blendsthat undergo an irreversible degradation may also be suitable, if theproducts of the degradation do not undesirably interfere with either theconductivity of the filter cake or with the production of any of thefluids from the subterranean formation.

Specific examples of suitable particulates may include, but not belimited to, BARACARB® particulates (ground marble, available fromHalliburton Energy Services, Inc.) including BARACARB® 5, BARACARB® 25,BARACARB® 150, BARACARB® 600, BARACARB® 1200; STEELSEAL® particulates(resilient graphitic carbon, available from Halliburton Energy Services,Inc.) including STEELSEAL® powder, STEELSEAL® 50, STEELSEAL® 150,STEELSEAL® 400 and STEELSEAL® 1000; WALL-NUT® particulates (groundwalnut shells, available from Halliburton Energy Services, Inc.)including WALL-NUT® M, WALL-NUT® coarse, WALL-NUT® medium, and WALL-NUT®fine; BARAPLUG® (sized salt water, available from Halliburton EnergyServices, Inc.) including BARAPLUG® 20, BARAPLUG® 50, and BARAPLUG®3/300; BARAFLAKE® (calcium carbonate and polymers, available fromHalliburton Energy Services, Inc.); and the like; and any combinationthereof.

Further examples of suitable fibers may include, but not be limited to,fibers of cellulose including viscose cellulosic fibers, oil coatedcellulosic fibers, and fibers derived from a plant product like paperfibers; carbon including carbon fibers; melt-processed inorganic fibersincluding basalt fibers, woolastonite fibers, non-amorphous metallicfibers, metal oxide fibers, mixed metal oxide fibers, ceramic fibers,and glass fibers; polymeric fibers including polypropylene fibers andpoly(acrylic nitrile) fibers; metal oxide fibers; mixed metal oxidefibers; and the like; and any combination thereof. Examples may alsoinclude, but not be limited to, PAN fibers, i.e., carbon fibers derivedfrom poly(acrylonitrile); PANEX® fibers (carbon fibers, available fromZoltek) including PANEX® 32, PANEX® 35-0.125″, and PANEX® 35-0.25″;PANOX® (oxidized PAN fibers, available from SGL Group); rayon fibersincluding BDF™ 456 (rayon fibers, available from Halliburton EnergyServices, Inc.); poly(lactide) (“PLA”) fibers; alumina fibers;cellulosic fibers; BAROFIBRE® fibers including BAROFIBRE® and BAROFIBRE®C (cellulosic fiber, available from Halliburton Energy Services, Inc.);and the like; and any combination thereof.

In some embodiments, the concentration of a particulate WSM in awellbore strengthening fluid (or drilling fluid) may range from a lowerlimit of about 0.01 pounds per barrel (“PPB”), 0.05 PPB, 0.1 PPB, 0.5PPB, 1 PPB, 3 PPB, 5 PPB, 10 PPB, 25 PPB, or 50 PPB to an upper limit ofabout 150 PPB, 100 PPB, 75 PPB, 50 PPB, 25 PPB, 10 PPB, 5 PPB, 4 PPB, 3PPB, 2 PPB, 1 PPB, or 0.5 PPB, and wherein the particulate WSMconcentration may range from any lower limit to any upper limit andencompass any subset therebetween. In some embodiments, theconcentration of a fiber WSM in a wellbore strengthening fluid (ordrilling fluid) may range from a lower limit of about 0.01 PPB, 0.05PPB, 0.1 PPB, 0.5 PPB, 1 PPB, 3 PPB, 5 PPB, or 10 PPB to an upper limitof about 120 PPB, 100 PPB, 75 PPB, 50 PPB, 20 PPB, 10 PPB, 5 PPB, 4 PPB,3 PPB, 2 PPB, 1 PPB, or 0.5 PPB, and wherein the fiber WSM concentrationmay range from any lower limit to any upper limit and encompass anysubset therebetween. One skilled in the art, with the benefit of thisdisclosure, should understand that the concentrations of the particulateand/or fiber WSM can effect the viscosity of the wellbore strengtheningfluid, and therefore should be adjusted to ensure proper delivery ofsaid particulate and/or fiber WSM into the wellbore.

Suitable fluids for suspending WSM and suitable base fluids for use inconjunction with the present invention may comprise oil-based fluids,aqueous-based fluids, aqueous-miscible fluids, water-in-oil emulsions,or oil-in-water emulsions. Suitable oil-based fluids may includealkanes, olefins, aromatic organic compounds, cyclic alkanes, paraffins,diesel fluids, mineral oils, desulfurized hydrogenated kerosenes, andany combination thereof. Suitable aqueous-based fluids may include freshwater, saltwater (e.g., water containing one or more salts dissolvedtherein), brine (e.g., saturated salt water), seawater, and anycombination thereof. Suitable aqueous-miscible fluids may include, butnot be limited to, alcohols, e.g., methanol, ethanol, n-propanol,isopropanol, n-butanol, sec-butanol, isobutanol, and t-butanol;glycerins; glycols, e.g., polyglycols, propylene glycol, and ethyleneglycol; polyglycol amines; polyols; any derivative thereof; any incombination with salts, e.g., sodium chloride, calcium chloride, calciumbromide, zinc bromide, potassium carbonate, sodium formate, potassiumformate, cesium formate, sodium acetate, potassium acetate, calciumacetate, ammonium acetate, ammonium chloride, ammonium bromide, sodiumnitrate, potassium nitrate, ammonium nitrate, ammonium sulfate, calciumnitrate, sodium carbonate, potassium carbonate, and any combinationthereof; any in combination with an aqueous-based fluid; and anycombination thereof. Suitable water-in-oil emulsions, also known asinvert emulsions, may have an oil-to-water ratio from a lower limit ofgreater than about 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, or 80:20 toan upper limit of less than about 100:0, 95:5, 90:10, 85:15, 80:20,75:25, 70:30, or 65:35 by volume in the base treatment fluid, where theamount may range from any lower limit to any upper limit and encompassany subset therebetween. Examples of suitable invert emulsions includethose disclosed in U.S. Pat. No. 5,905,061, U.S. Pat. No. 5,977,031, andU.S. Pat. No. 6,828,279, each of which are incorporated herein byreference. It should be noted that for water-in-oil and oil-in-wateremulsions, any mixture of the above may be used including the waterbeing an aqueous-miscible fluid.

In some embodiments, a wellbore strengthening fluid (or a drillingfluid) may optionally comprise a polar organic molecule. In someembodiments, the addition of a polar organic molecule to an oil-basedfluid may advantageously increase the efficacy of the WSM therein. Polarorganic molecules may be any molecule with a dielectric constant greaterthan about 2, e.g., diethyl ether (dielectric constant of 4.3), ethylamine (dielectric constant of 8.7), pyridine (dielectric constant of12.3), and acetone (dielectric constant of 20.7). Polar organicmolecules suitable for use in the present invention may include anypolar organic molecule including protic and aprotic organic molecules.Suitable protic molecules may include, but not be limited to, organicmolecules with at least one functional group to include alcohols,aldehydes, acids, amines, amides, thiols, and any combination thereof.Suitable aprotic molecules may include, but not be limited to, organicmolecules with at least one functional group to include esters, ethers,nitrites, nitriles, ketones, sulfoxides, halogens, and any combinationthereof. Suitable polar organic molecules may be cyclic compoundsincluding, but not limited to, pyrrole, pyridine, furan, any derivativethereof, and any combination thereof. Suitable polar organic moleculesmay include an organic molecule with multiple functional groupsincluding mixtures of protic and aprotic groups. In some embodiments, adrilling fluid may comprise multiple polar organic molecules. In someembodiments, a polar organic molecule may be present in a wellborestrengthening fluid (or a drilling fluid) in an amount from a lowerlimit of about 0.01%, 0.1%, 0.5%, 1%, 5%, or 10% to an upper limit ofabout 100%, 90%, 75%, 50%, 25%, 20%, 15%, 10%, 5%, 1%, 0.5%, or 0.1% byvolume of the wellbore strengthening fluid (or the drilling fluid), andwherein the polar organic molecule concentration may range from anylower limit to any upper limit and encompass any subset therebetween.

In some embodiments, other additives may optionally be included inwellbore strengthening fluids (or drilling fluids). Examples of suchadditives may include, but are not limited to, salts, weighting agents,inert solids, fluid loss control agents, emulsifiers, dispersion aids,corrosion inhibitors, emulsion thinners, emulsion thickeners,viscosifying agents, surfactants, particulates, proppants, lostcirculation materials, pH control additives, foaming agents, breakers,biocides, crosslinkers, stabilizers, chelating agents, scale inhibitors,gas, mutual solvents, oxidizers, reducers, and any combination thereof.A person of ordinary skill in the art, with the benefit of thisdisclosure, will recognize when an additive should be included in awellbore strengthening fluid and/or drilling fluid, as well as anappropriate amount of said additive to include.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered,combined, or modified and all such variations are considered within thescope and spirit of the present invention. The invention illustrativelydisclosed herein suitably may be practiced in the absence of any elementthat is not specifically disclosed herein and/or any optional elementdisclosed herein. While compositions and methods are described in termsof “comprising,” “containing,” or “including” various components orsteps, the compositions and methods can also “consist essentially of” or“consist of” the various components and steps. All numbers and rangesdisclosed above may vary by some amount. Whenever a numerical range witha lower limit and an upper limit is disclosed, any number and anyincluded range falling within the range is specifically disclosed. Inparticular, every range of values (of the form, “from about a to aboutb,” or, equivalently, “from approximately a to b,” or, equivalently,“from approximately a-b”) disclosed herein is to be understood to setforth every number and range encompassed within the broader range ofvalues. Also, the terms in the claims have their plain, ordinary meaningunless otherwise explicitly and clearly defined by the patentee.Moreover, the indefinite articles “a” or “an,” as used in the claims,are defined herein to mean one or more than one of the element that itintroduces. If there is any conflict in the usages of a word or term inthis specification and one or more patent or other documents that may beincorporated herein by reference, the definitions that are consistentwith this specification should be adopted.

The invention claimed is:
 1. A tool comprising: an implement thatcomprises at least one passageway that models an opening in asubterranean formation, the passageway comprising an entry port on afirst end of an object, an exit port at an opposing end of the object,and a wall extending from the entry port to the exit port; and at leastone sensor in or on the implement proximal to the wall of thepassageway.
 2. The tool of claim 1, wherein the at least one sensor isselected from the group consisting of a force gauge, a load cell, apiezoelectric sensor, a magnetic sensor, an ultrasonic sensor, and astrain gauge.
 3. The tool of claim 1, wherein the at least one sensor isembedded in the implement.
 4. The tool of claim 1, wherein the at leastone sensor is disposed on the wall of the passageway.
 5. The tool ofclaim 1, wherein the implement comprises a holder and an insert capableof operably mating with a holder, and wherein the insert comprises theat least one sensor.
 6. The tool of claim 1, wherein the passageway hasat least one adjustable wall.
 7. The tool of claim 1, wherein thepassageway is a tapered slot passageway with the entry port has asmallest dimension between about 1000 microns and about 6000 microns,the exit port with a smallest dimension between about 100 microns andabout 3000 microns, and the smallest dimension of the exit port is lessthan the smallest dimension of the entry port.
 8. The tool of claim 1,wherein the entry port and the exit port have a slit shape.
 9. The toolof claim 1, wherein the entry port and the exit port have a shape of anartificial or man-made fracture.
 10. The tool of claim 1, wherein thepassageway is a natural fracture in a core sample.
 11. A toolcomprising: an implement that comprises a tapered slot that models anopening in a subterranean formation, the passageway comprising an entryport having a slit shape with a smallest dimension between about 1000microns and about 6000 microns on a first end of an object, an exit porthaving a slit shape with a smallest dimension between about 100 micronsand about 3000 microns at an opposing end of the object, and a wallextending from the entry port to the exit port, wherein the smallestdimension of the exit port is less than the smallest dimension of theentry port; and at least one sensor in or on the implement proximal tothe wall of the passageway.
 12. The tool of claim 11, wherein the atleast one sensor is selected from the group consisting of a force gauge,a load cell, a piezoelectric sensor, a magnetic sensor, an ultrasonicsensor, and a strain gauge.
 13. The tool of claim 11, wherein the atleast one sensor is embedded in the implement.
 14. The tool of claim 11,wherein the at least one sensor is disposed on the wall of thepassageway.
 15. The tool of claim 11, wherein the implement comprises aholder and an insert capable of operably mating with a holder, andwherein the insert comprises the at least one sensor.
 16. The tool ofclaim 11, wherein the passageway has at least one adjustable wall.